This proposal describes the design and testing of new enzyme-based amperometric sensors for the neurotransmitters acetylcholine, glutamate, and aspartate, in which electrical communication between the flavin redox centers of an oxidase and an electrode is achieved via a network of donor- acceptor relays chemically bound to a flexible siloxane polymer. Because the electron transfer mediators are covalently attached to an insoluble polymer and cannot diffuse away from the electrode, these sensors should be suitable for implantation, and thus would be useful for in vivo neurochemical research. The proposed research plan for Phase I concerns the development of these sensors through the following approach: construct redox polymer-modified sensors containing acetylcholinesterase and choline oxidase (for acetylcholine detection), L-glutamate oxidase (for glutamate detection), and L-aspartate oxidase (for aspartate detection); by varying the number of polymer-bound electron relays, optimize the sensor response to substrate, minimize the operating voltage (in order to decrease any interface due to easily oxidizable species), and eliminate any decrease in response due to dissolved oxygen. In addition, in order to increase the response to acetylcholine, eliminate interference due to spurious anionic species, and prevent sensor fouling, a commercially available anionic poly(ester sulfonic acid) will be used to coat the acetylcholine sensor.